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 * @param {number[]} nums
 * @return {number[]}
 */</span>
 <span class="token keyword">var</span> <span class="token function-variable function">sortArray</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">nums</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token keyword">const</span> <span class="token function-variable function">partition</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token parameter">arr</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token comment">// 生成0-arr.length-1的随机数</span>
        <span class="token keyword">let</span> mid<span class="token operator">=</span>Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">*</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">)</span>
        <span class="token keyword">let</span> midValue<span class="token operator">=</span>arr<span class="token punctuation">[</span>mid<span class="token punctuation">]</span>

        <span class="token keyword">let</span> left<span class="token operator">=</span><span class="token number">0</span>
        <span class="token keyword">let</span> right<span class="token operator">=</span>arr<span class="token punctuation">.</span>length<span class="token operator">-</span><span class="token number">1</span>

        <span class="token keyword">while</span><span class="token punctuation">(</span>left<span class="token operator">&lt;=</span>right<span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">while</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>left<span class="token punctuation">]</span><span class="token operator">&lt;</span>midValue<span class="token punctuation">)</span><span class="token punctuation">{</span>
                left<span class="token operator">++</span>
            <span class="token punctuation">}</span>

            <span class="token keyword">while</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>right<span class="token punctuation">]</span><span class="token operator">&gt;</span>midValue<span class="token punctuation">)</span><span class="token punctuation">{</span>
                right<span class="token operator">--</span>
            <span class="token punctuation">}</span>

            <span class="token keyword">if</span><span class="token punctuation">(</span>left<span class="token operator">&lt;=</span>right<span class="token punctuation">)</span><span class="token punctuation">{</span>
                <span class="token comment">// 交换left和right下标对应的元素</span>
                <span class="token keyword">let</span> temp<span class="token operator">=</span>arr<span class="token punctuation">[</span>left<span class="token punctuation">]</span>
                arr<span class="token punctuation">[</span>left<span class="token punctuation">]</span><span class="token operator">=</span>arr<span class="token punctuation">[</span>right<span class="token punctuation">]</span>
                arr<span class="token punctuation">[</span>right<span class="token punctuation">]</span><span class="token operator">=</span>temp

                left<span class="token operator">++</span>
                right<span class="token operator">--</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>

        <span class="token keyword">return</span> right
    <span class="token punctuation">}</span>

    <span class="token comment">// 原地快排</span>

    <span class="token keyword">const</span> <span class="token function-variable function">quickSort</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token parameter">arr</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>

        <span class="token keyword">if</span><span class="token punctuation">(</span>arr<span class="token punctuation">.</span>length<span class="token operator">&lt;=</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token keyword">return</span> arr

        <span class="token keyword">let</span> pivot<span class="token operator">=</span><span class="token function">partition</span><span class="token punctuation">(</span>arr<span class="token punctuation">)</span>
        
        <span class="token keyword">let</span> leftArr<span class="token operator">=</span>arr<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span>pivot<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">)</span>
        <span class="token keyword">let</span> rightArr<span class="token operator">=</span>arr<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span>pivot<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">,</span>arr<span class="token punctuation">.</span>length<span class="token punctuation">)</span>

        <span class="token keyword">let</span> orderLeft<span class="token operator">=</span><span class="token function">quickSort</span><span class="token punctuation">(</span>leftArr<span class="token punctuation">)</span>
        <span class="token keyword">let</span> orderRight<span class="token operator">=</span><span class="token function">quickSort</span><span class="token punctuation">(</span>rightArr<span class="token punctuation">)</span>

        <span class="token keyword">return</span> <span class="token punctuation">[</span><span class="token operator">...</span>orderLeft<span class="token punctuation">,</span><span class="token operator">...</span>orderRight<span class="token punctuation">]</span>
    <span class="token punctuation">}</span>

    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span> <span class="token function">quickSort</span><span class="token punctuation">(</span>nums<span class="token punctuation">)</span><span class="token punctuation">)</span>

    

<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token function">sortArray</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">9</span><span class="token punctuation">,</span><span class="token number">7</span><span class="token punctuation">,</span><span class="token number">8</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">,</span><span class="token number">13</span><span class="token punctuation">,</span><span class="token number">6</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br></div></div><h3 id="计数排序模板"><a href="#计数排序模板" class="header-anchor">#</a> 计数排序模板</h3> <ul><li>适用于n较小的情况</li></ul> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[]} nums
 * @return {number[]}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">sortArray</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">nums</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 基数排序</span>

    <span class="token keyword">let</span> arr<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>

    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token operator">-</span><span class="token number">50000</span><span class="token punctuation">;</span>i<span class="token operator">&lt;=</span><span class="token number">50000</span><span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">=</span><span class="token number">0</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>nums<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        arr<span class="token punctuation">[</span>nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token operator">++</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">let</span> res<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    <span class="token comment">// let n=0</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token operator">-</span><span class="token number">50000</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span><span class="token number">500001</span><span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token comment">// if(arr[i]===undefined) continue</span>
        <span class="token keyword">while</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">&gt;</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span>
            arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">--</span>
            <span class="token comment">// n++</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">return</span> res

<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br></div></div><h4 id="_1122-数组的相对排序"><a href="#_1122-数组的相对排序" class="header-anchor">#</a> <a href="https://leetcode.cn/problems/relative-sort-array/description/" target="_blank" rel="noopener noreferrer">1122. 数组的相对排序<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></h4> <p>给你两个数组，<code>arr1</code> 和 <code>arr2</code>，<code>arr2</code> 中的元素各不相同，<code>arr2</code> 中的每个元素都出现在 <code>arr1</code> 中。</p> <p>对 <code>arr1</code> 中的元素进行排序，使 <code>arr1</code> 中项的相对顺序和 <code>arr2</code> 中的相对顺序相同。未在 <code>arr2</code> 中出现过的元素需要按照升序放在 <code>arr1</code> 的末尾。</p> <p><strong>示例 1：</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入：arr1 = [2,3,1,3,2,4,6,7,9,2,19], arr2 = [2,1,4,3,9,6]
输出：[2,2,2,1,4,3,3,9,6,7,19]
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>示例  2:</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入：arr1 = [28,6,22,8,44,17], arr2 = [22,28,8,6]
输出：[22,28,8,6,17,44]
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>提示：</strong></p> <ul><li><code>1 &lt;= arr1.length, arr2.length &lt;= 1000</code></li> <li><code>0 &lt;= arr1[i], arr2[i] &lt;= 1000</code></li> <li><code>arr2</code> 中的元素 <code>arr2[i]</code> <strong>各不相同</strong></li> <li><code>arr2</code> 中的每个元素 <code>arr2[i]</code> 都出现在 <code>arr1</code> 中</li></ul> <h5 id="完整代码"><a href="#完整代码" class="header-anchor">#</a> 完整代码</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[]} arr1
 * @param {number[]} arr2
 * @return {number[]}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">relativeSortArray</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">arr1<span class="token punctuation">,</span> arr2</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 对arr1进行计数排序</span>

    <span class="token comment">// 遍历arr2中的数组，把有计数的输出，计数减为0</span>

    <span class="token comment">// 再遍历arr，把没出现在arr2的也输出</span>

    <span class="token keyword">let</span> arr<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Array</span><span class="token punctuation">(</span><span class="token number">1001</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">fill</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span>

    <span class="token keyword">let</span> res<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    arr1<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        arr<span class="token punctuation">[</span>item<span class="token punctuation">]</span><span class="token operator">++</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span> 

    arr2<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">while</span><span class="token punctuation">(</span>arr<span class="token punctuation">[</span>item<span class="token punctuation">]</span><span class="token operator">&gt;</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            arr<span class="token punctuation">[</span>item<span class="token punctuation">]</span><span class="token operator">--</span>
            res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>item<span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    arr<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item<span class="token punctuation">,</span>index</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">while</span><span class="token punctuation">(</span>item<span class="token operator">&gt;</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            item<span class="token operator">--</span>
            res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>index<span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    <span class="token keyword">return</span> res


<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br></div></div><h4 id="_56-合并区间"><a href="#_56-合并区间" class="header-anchor">#</a> <a href="https://leetcode.cn/problems/merge-intervals/description/" target="_blank" rel="noopener noreferrer">56. 合并区间<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></h4> <p>以数组 <code>intervals</code> 表示若干个区间的集合，其中单个区间为 <code>intervals[i] = [starti, endi]</code> 。请你合并所有重叠的区间，并返回 <em>一个不重叠的区间数组，该数组需恰好覆盖输入中的所有区间</em> 。</p> <p><strong>示例 1：</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入：intervals = [[1,3],[2,6],[8,10],[15,18]]
输出：[[1,6],[8,10],[15,18]]
解释：区间 [1,3] 和 [2,6] 重叠, 将它们合并为 [1,6].
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>示例 2：</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入：intervals = [[1,4],[4,5]]
输出：[[1,5]]
解释：区间 [1,4] 和 [4,5] 可被视为重叠区间。
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>提示：</strong></p> <ul><li><code>1 &lt;= intervals.length &lt;= 104</code></li> <li><code>intervals[i].length == 2</code></li> <li><code>0 &lt;= starti &lt;= endi &lt;= 104</code></li></ul> <h5 id="解题思路"><a href="#解题思路" class="header-anchor">#</a> 解题思路</h5> <div class="language-shell line-numbers-mode"><pre class="language-shell"><code><span class="token number">1</span>. 状态空间暴力，区间没有访问过，开始往后连接，连接过的不能用，循环所有没有访问过的空间，当不能在向下连接时，输出结果

<span class="token number">2</span>. 双关键字排序，即区间l<span class="token operator"><span class="token file-descriptor important">1</span>&lt;</span><span class="token operator">=</span>l2 r<span class="token operator"><span class="token file-descriptor important">1</span>&lt;</span><span class="token operator">=</span>r2 ,排好序后，判断是否可以向后连接，不行就另起一段，行就放入答案

<span class="token number">3</span>. 差分数组
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><h5 id="状态空间暴力"><a href="#状态空间暴力" class="header-anchor">#</a> 状态空间暴力</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[][]} intervals
 * @return {number[][]}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">merge</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">intervals</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 状态空间暴力</span>

    <span class="token comment">// 先对intervals进行部分排序</span>

    intervals<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span>b</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">-</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>


    <span class="token keyword">let</span> res<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    
    <span class="token comment">// 递归，合并或者不能合并，看能走多远</span>
    <span class="token keyword">let</span> visited<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Array</span><span class="token punctuation">(</span>intervals<span class="token punctuation">.</span>length<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">fill</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">)</span>

    <span class="token keyword">let</span> mostDist<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    <span class="token keyword">const</span> <span class="token function-variable function">dfs</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token parameter">arr</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>

        mostDist<span class="token operator">=</span>arr
        
        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator">&lt;</span>intervals<span class="token punctuation">.</span>length<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>

            <span class="token keyword">if</span><span class="token punctuation">(</span>visited<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token keyword">continue</span>
            <span class="token comment">// visited[i]=true</span>
            <span class="token comment">// 判断是否能够合并</span>
            <span class="token keyword">if</span><span class="token punctuation">(</span>intervals<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">&gt;=</span>arr<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">&amp;&amp;</span>intervals<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">&lt;=</span>arr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                visited<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">=</span><span class="token boolean">true</span>
                <span class="token comment">// 合并</span>
                <span class="token keyword">let</span> newArr<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Array</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
                newArr<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">=</span>Math<span class="token punctuation">.</span><span class="token function">min</span><span class="token punctuation">(</span>intervals<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">,</span>arr<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
                newArr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">=</span>Math<span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>intervals<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">,</span>arr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
                <span class="token function">dfs</span><span class="token punctuation">(</span>newArr<span class="token punctuation">)</span>
                <span class="token comment">// console.log(newArr)</span>
                <span class="token comment">// far</span>
                <span class="token keyword">if</span><span class="token punctuation">(</span>mostDist<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">&lt;</span>newArr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                    mostDist<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">=</span>newArr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span>
                <span class="token punctuation">}</span>
                <span class="token keyword">break</span>
            <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
                <span class="token comment">// 走到底了，不能在合了 </span>
                <span class="token keyword">break</span>
            <span class="token punctuation">}</span>

        <span class="token punctuation">}</span> 

        <span class="token keyword">return</span> mostDist
    <span class="token punctuation">}</span>


    
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> j<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>j<span class="token operator">&lt;</span>intervals<span class="token punctuation">.</span>length<span class="token punctuation">;</span>j<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span>visited<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
           mostDist<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
           visited<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token operator">=</span><span class="token boolean">true</span>
           res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>Array<span class="token punctuation">.</span><span class="token function">from</span><span class="token punctuation">(</span><span class="token function">dfs</span><span class="token punctuation">(</span>intervals<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// console.log(res)</span>
    <span class="token keyword">return</span> res

<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br><span class="line-number">62</span><br><span class="line-number">63</span><br><span class="line-number">64</span><br><span class="line-number">65</span><br><span class="line-number">66</span><br><span class="line-number">67</span><br></div></div><h5 id="双关键字排序-判定"><a href="#双关键字排序-判定" class="header-anchor">#</a> 双关键字排序+判定</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[][]} intervals
 * @return {number[][]}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">merge</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">intervals</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 区间合并</span>

    <span class="token comment">// 双关键字排序</span>
    <span class="token comment">// 我们先把区间进行排序，l1&lt;l2  l1=l2时  排序r1&lt;r2</span>
    intervals<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span>b</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">-</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">||</span> <span class="token punctuation">(</span>a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">===</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">&amp;&amp;</span>a<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">-</span>b<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span> 

    <span class="token comment">// console.log(intervals)</span>

    <span class="token comment">// 遍历区间</span>
    <span class="token comment">// 看最远能延续到哪里</span>

    <span class="token comment">// [1,3]  3</span>
    <span class="token comment">// [2,6]  6</span>

    <span class="token comment">// 另起一段</span>
    <span class="token comment">// [8,10] 10</span>

    <span class="token comment">// 另起一段</span>
    <span class="token comment">// [15,18] 18</span>

    <span class="token comment">// 记录起点</span>
    <span class="token keyword">let</span> left<span class="token operator">=</span><span class="token operator">-</span><span class="token number">1</span> 
    <span class="token comment">// 记录最远的距离</span>
    <span class="token keyword">let</span> far<span class="token operator">=</span><span class="token operator">-</span><span class="token number">1</span>

    <span class="token keyword">let</span> res<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    intervals<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">let</span> start<span class="token operator">=</span>item<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span>
        <span class="token keyword">let</span> end<span class="token operator">=</span>item<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span>

        <span class="token keyword">if</span><span class="token punctuation">(</span>start<span class="token operator">&lt;=</span>far<span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token comment">// 可以延续</span>
            far<span class="token operator">=</span>Math<span class="token punctuation">.</span><span class="token function">max</span><span class="token punctuation">(</span>far<span class="token punctuation">,</span>end<span class="token punctuation">)</span>
        <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
            <span class="token comment">// 不可延续，另起一段</span>
            <span class="token keyword">if</span><span class="token punctuation">(</span>far<span class="token operator">&gt;=</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">[</span>left<span class="token punctuation">,</span>far<span class="token punctuation">]</span><span class="token punctuation">)</span>
            <span class="token punctuation">}</span>
            left<span class="token operator">=</span>start
            far<span class="token operator">=</span>end
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    <span class="token comment">// 最后可能一直在连续，需要把最后一段加入</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>far<span class="token operator">&gt;=</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
        res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">[</span>left<span class="token punctuation">,</span>far<span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token keyword">return</span> res

<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br></div></div><h5 id="差分数组"><a href="#差分数组" class="header-anchor">#</a> 差分数组</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[][]} intervals
 * @return {number[][]}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">merge</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">intervals</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 使用计数排序的思想进行区间的合并</span>

    <span class="token comment">// [1,3] 1 2 3</span>

    <span class="token comment">// [2,6] 2,3,4,5,6</span>

    <span class="token comment">// [8,10] 8,9,10</span>

    <span class="token comment">// [15,18] 15,16,17,18</span>

    <span class="token comment">// 优化版本</span>

    <span class="token comment">// 使用差分数组</span>

    <span class="token comment">// 1 2 3 4 5 6 7 8 9 10</span>
    <span class="token comment">// 差分数组</span>
    <span class="token comment">// 1 1 1 1 1 1 1 1 1 1</span>
    
    <span class="token comment">// 我们覆盖[1,3]，即1-3都加上1</span>
    <span class="token comment">// 2 1 1 0</span>
    <span class="token comment">// 实际上只需要在1 +1   在4处-1</span>


    <span class="token comment">// 定义差分事件，+1 开始覆盖</span>
    <span class="token comment">// -1  结束覆盖</span>

    <span class="token keyword">let</span> m<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>

    <span class="token comment">// 定义开始覆盖下标到 事件的映射</span>

    intervals<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        m<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">[</span>item<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">,</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
        m<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">[</span>item<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    <span class="token comment">// 根据开始覆盖的事件在前进行排序</span>
    m<span class="token punctuation">.</span><span class="token function">sort</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span>b</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">return</span> a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">-</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">||</span><span class="token punctuation">(</span>a<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">===</span>b<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">&amp;&amp;</span>a<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token operator">-</span>b<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>m<span class="token punctuation">)</span>

    <span class="token comment">// 定义一个count值，如果count 0-1 说明开始覆盖</span>

    <span class="token comment">// 1-0 结束覆盖，输出left-far</span>
    <span class="token keyword">let</span> count<span class="token operator">=</span><span class="token number">0</span>

    <span class="token keyword">let</span> left<span class="token operator">=</span><span class="token operator">-</span><span class="token number">1</span>
    <span class="token keyword">let</span> far<span class="token operator">=</span><span class="token operator">-</span><span class="token number">1</span>
    <span class="token keyword">let</span> res<span class="token operator">=</span><span class="token punctuation">[</span><span class="token punctuation">]</span>
    m<span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">item</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>count<span class="token operator">===</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            left<span class="token operator">=</span>item<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span>
        <span class="token punctuation">}</span>

        count<span class="token operator">+=</span>item<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span>

        <span class="token keyword">if</span><span class="token punctuation">(</span>count<span class="token operator">===</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            far<span class="token operator">=</span>item<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token operator">-</span><span class="token number">1</span>
            res<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token punctuation">[</span>left<span class="token punctuation">,</span>far<span class="token punctuation">]</span><span class="token punctuation">)</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span>

    <span class="token keyword">return</span> res
   

<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br><span class="line-number">62</span><br><span class="line-number">63</span><br><span class="line-number">64</span><br><span class="line-number">65</span><br><span class="line-number">66</span><br><span class="line-number">67</span><br><span class="line-number">68</span><br><span class="line-number">69</span><br><span class="line-number">70</span><br><span class="line-number">71</span><br><span class="line-number">72</span><br><span class="line-number">73</span><br></div></div><h4 id="_493-翻转对"><a href="#_493-翻转对" class="header-anchor">#</a> <a href="https://leetcode.cn/problems/reverse-pairs/description/" target="_blank" rel="noopener noreferrer">493. 翻转对<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></h4> <p>给定一个数组 <code>nums</code> ，如果 <code>i &lt; j</code> 且 <code>nums[i] &gt; 2*nums[j]</code> 我们就将 <code>(i, j)</code> 称作一个*<strong>重要翻转对*</strong>。</p> <p>你需要返回给定数组中的重要翻转对的数量。</p> <p><strong>示例 1:</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入: [1,3,2,3,1]
输出: 2
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>示例 2:</strong></p> <div class="language- line-numbers-mode"><pre class="language-text"><code>输入: [2,4,3,5,1]
输出: 3
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p><strong>注意:</strong></p> <ol><li>给定数组的长度不会超过<code>50000</code>。</li> <li>输入数组中的所有数字都在32位整数的表示范围内。</li></ol> <h5 id="解题思路-2"><a href="#解题思路-2" class="header-anchor">#</a> 解题思路</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token number">1.</span>  暴力，超时
<span class="token number">2.</span> 条件判断，这里满足不等式i<span class="token operator">&lt;</span>j nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">&gt;</span><span class="token number">2</span><span class="token operator">*</span>nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">,</span> 但是下标和值的不等式矛盾，用二分不能兼顾两边
<span class="token number">3.</span> 一般遇到这边的，使用归并排序，减小规模，减低时间复杂度求解
<span class="token number">4.</span> 满足条件的情况，分为左边部分满足的，右边部分满足的，和
	跨左右部分满足的，因为递归的最后面（只存在左右跨部分满足的（关键））
    
<span class="token number">5.</span> 是否满足，双指针烧苗，i在左边，j在右边，限固定i，看j是否满足
<span class="token number">6.</span> 双指针的优化 nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">&gt;</span><span class="token number">2</span><span class="token operator">*</span>nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span>  ，是不是下标在i右边的，也满足，因为数组有序
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><h5 id="完整代码-2"><a href="#完整代码-2" class="header-anchor">#</a> 完整代码</h5> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token comment">/**
 * @param {number[]} nums
 * @return {number}
 */</span>
<span class="token keyword">var</span> <span class="token function-variable function">reversePairs</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">nums</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment">// 满足两种不等式i&lt;j</span>
    <span class="token comment">// nus[i]&gt;2*nums[j]</span>

    <span class="token comment">// 这两种不等式发生了冲突</span>

    <span class="token comment">// 如果不冲突，二分</span>
    <span class="token comment">// 冲突了，考虑使用归并排序解决</span>

    <span class="token keyword">let</span> ans<span class="token operator">=</span><span class="token number">0</span>

    <span class="token keyword">const</span> <span class="token function-variable function">merge</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token parameter">arr<span class="token punctuation">,</span>left<span class="token punctuation">,</span>mid<span class="token punctuation">,</span>right</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>

        <span class="token comment">// 临时数组</span>
        <span class="token keyword">let</span> temp<span class="token operator">=</span><span class="token keyword">new</span> <span class="token class-name">Array</span><span class="token punctuation">(</span>right<span class="token operator">-</span>left<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">)</span>

        <span class="token keyword">let</span> i<span class="token operator">=</span>left
        <span class="token keyword">let</span> j<span class="token operator">=</span>mid<span class="token operator">+</span><span class="token number">1</span>

        <span class="token comment">// 合并两个有序数组</span>
        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> k<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>k<span class="token operator">&lt;</span>temp<span class="token punctuation">.</span>length<span class="token punctuation">;</span>k<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            
            <span class="token keyword">if</span><span class="token punctuation">(</span>j<span class="token operator">&gt;</span>right<span class="token operator">||</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">&lt;=</span>arr<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token operator">&amp;&amp;</span>i<span class="token operator">&lt;=</span>mid<span class="token punctuation">)</span><span class="token punctuation">{</span>
                temp<span class="token punctuation">[</span>k<span class="token punctuation">]</span><span class="token operator">=</span>arr<span class="token punctuation">[</span>i<span class="token operator">++</span><span class="token punctuation">]</span>
            <span class="token punctuation">}</span><span class="token keyword">else</span><span class="token punctuation">{</span>
                temp<span class="token punctuation">[</span>k<span class="token punctuation">]</span><span class="token operator">=</span>arr<span class="token punctuation">[</span>j<span class="token operator">++</span><span class="token punctuation">]</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>

        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> k<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>k<span class="token operator">&lt;</span>temp<span class="token punctuation">.</span>length<span class="token punctuation">;</span>k<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            arr<span class="token punctuation">[</span>left<span class="token operator">+</span>k<span class="token punctuation">]</span><span class="token operator">=</span>temp<span class="token punctuation">[</span>k<span class="token punctuation">]</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>

    <span class="token comment">// 原地归并，不生产子数组</span>

    <span class="token keyword">const</span> <span class="token function-variable function">mergeSort</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token parameter">arr<span class="token punctuation">,</span>left<span class="token punctuation">,</span>right</span><span class="token punctuation">)</span><span class="token operator">=&gt;</span><span class="token punctuation">{</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>left<span class="token operator">&gt;=</span>right<span class="token punctuation">)</span> <span class="token keyword">return</span>
        <span class="token keyword">let</span> mid<span class="token operator">=</span>Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span><span class="token punctuation">(</span>left<span class="token operator">+</span>right<span class="token punctuation">)</span><span class="token operator">/</span><span class="token number">2</span><span class="token punctuation">)</span>

        <span class="token function">mergeSort</span><span class="token punctuation">(</span>arr<span class="token punctuation">,</span>left<span class="token punctuation">,</span>mid<span class="token punctuation">)</span>
        <span class="token function">mergeSort</span><span class="token punctuation">(</span>arr<span class="token punctuation">,</span>mid<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">,</span>right<span class="token punctuation">)</span>

        <span class="token comment">// 双指针扫描</span>

        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">let</span> i<span class="token operator">=</span>left<span class="token punctuation">,</span>j<span class="token operator">=</span>mid<span class="token punctuation">;</span>i<span class="token operator">&lt;=</span>mid<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            <span class="token keyword">while</span><span class="token punctuation">(</span>j<span class="token operator">&lt;</span>right<span class="token operator">&amp;&amp;</span>arr<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token operator">&gt;</span><span class="token number">2</span><span class="token operator">*</span>arr<span class="token punctuation">[</span>j<span class="token operator">+</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
                j<span class="token operator">++</span>
            <span class="token punctuation">}</span>

            ans<span class="token operator">+=</span><span class="token punctuation">(</span>j<span class="token operator">-</span>mid<span class="token punctuation">)</span>
        <span class="token punctuation">}</span>

        <span class="token function">merge</span><span class="token punctuation">(</span>arr<span class="token punctuation">,</span>left<span class="token punctuation">,</span>mid<span class="token punctuation">,</span>right<span class="token punctuation">)</span>
    <span class="token punctuation">}</span>

    <span class="token function">mergeSort</span><span class="token punctuation">(</span>nums<span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">,</span>nums<span class="token punctuation">.</span>length<span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span>
    <span class="token comment">// console.log(sort)</span>

    <span class="token keyword">return</span> ans
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br><span class="line-number">26</span><br><span class="line-number">27</span><br><span class="line-number">28</span><br><span class="line-number">29</span><br><span class="line-number">30</span><br><span class="line-number">31</span><br><span class="line-number">32</span><br><span class="line-number">33</span><br><span class="line-number">34</span><br><span class="line-number">35</span><br><span class="line-number">36</span><br><span class="line-number">37</span><br><span class="line-number">38</span><br><span class="line-number">39</span><br><span class="line-number">40</span><br><span class="line-number">41</span><br><span class="line-number">42</span><br><span class="line-number">43</span><br><span class="line-number">44</span><br><span class="line-number">45</span><br><span class="line-number">46</span><br><span class="line-number">47</span><br><span class="line-number">48</span><br><span class="line-number">49</span><br><span class="line-number">50</span><br><span class="line-number">51</span><br><span class="line-number">52</span><br><span class="line-number">53</span><br><span class="line-number">54</span><br><span class="line-number">55</span><br><span class="line-number">56</span><br><span class="line-number">57</span><br><span class="line-number">58</span><br><span class="line-number">59</span><br><span class="line-number">60</span><br><span class="line-number">61</span><br><span class="line-number">62</span><br><span class="line-number">63</span><br><span class="line-number">64</span><br><span class="line-number">65</span><br><span class="line-number">66</span><br></div></div></div></div>  <div class="page-edit"><div class="edit-link"><a href="https://github.com/linxin1123/vuepress-blog/edit/master/docs/07.算法/41.算法训练营/06.算法训练营-排序-cnblog.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2023/02/17, 11:29:32</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/9b8692/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">前缀和-差分-双指针（下）-cnblog</div></a> <a href="/pages/cbca68/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">二分</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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